Erectile dysfunction (ED) is a multifactorial disease that affects approximately 30 million American men and is continuing to increase along with the upsurge in diabetes, hypertension and cardiovascular disease. When first line and second line medications such as the phosphodiesterase 5 inhibitor class of medications or direct injections fail, surgical implantation of penile prostheses offers a permanent solution. Surgical implantation of prostheses is a known practical means of treating erectile dysfunction.
Two broad classes of penile prostheses are known in the prior art, the inflatable prosthesis and the semi-rigid prosthesis. The inflatable penile prosthesis aims to closely parallel a natural erection by shifting fluid from one area of the device, usually a reservoir, to the cylinders within the corpora cavernosa under hydraulic pressure to mimic the erect state. It relies on a closed system of reservoirs, pumps, valves and hydraulic pressure to produce a simulated erection sufficient for coitus. Consequently, the surgical implantation of this device is more complex is prone to mechanical failure. Indeed only 67 to 88% are fully functional at 10 years, (Selph et al. Penile prosthesis infection: approaches to prevention and treatment, Urol. Clin. N. Am. 2011; 38(2): 227-235). The advantages of the inflatable prosthesis are that it appears more physiologic and does not exert constant pressure on surrounding tissues when in the flaccid state reducing the risk of erosion.
In contrast, the semi-rigid strikes a balance between being rigid enough for penetration, but malleable enough to allow positioning downwards when not in use. The advantages are that the device is simple, reliable, involves a smaller dissection, has fewer parts, and requires minimal dexterity to use. The disadvantages are that it appears constantly erect. It exerts more force on the surrounding tissues and has increased risk for erosion.
Thus there is a need for a surgical solution for men with refractory erectile dysfunction that appears as physiologic as possible, yet remains discrete. The penile prosthesis we propose meets the criteria for a discrete, physiologic-appearing, penile implant that can be used to treat ED. It has the advantages of the malleable prosthesis in that it only requires implantable cylinders and has no scrotal pump or abdominal reservoir, but then also has the advantages of an inflatable penile prosthesis in that with application of heat can produce a simulated erection with expansion of the cylinders. It is different from existing thermal-based solutions in that this device takes advantage of the fine-tuned properties of commercially available nickel-titanium alloys, notably their hysteresis and reliable shape-memory properties, as opposed to phase changes.